Algorithms
When using the flat terrain version of the model, a release is simulated as a
series of puffs. There are three algorithms used for motion and dispersion of a
release in the atmosphere. The model, using the currently calculated parameters
of a release, internally decides on the use of an algorithm. The algorithms
cover: the jet phase of the release (all densities), the gravitational spread
when a denser-than-air cloud is on the ground, and all other cases (e.g. not
denser-than-air on ground and aloft clouds).
When using the complex terrain version of the model, the motion and dispersion of
the release is determined through the use of fundamental equations of
Navier-Stokes.
The fire algorithms calculate the thermal radiation impact from BLEVEs, Jet Fires
or Flares, and Pool Fires. For Jet and Pool Fires effects such as flame tilt are
calculated.
Two forms of explosion are allowed: Mechanical Failure and Vapor Cloud Explosions.
A Mechanical Failure simulation assumes a pressurized containment vessel fails
instantaneously, releasing a pressure wave. The Vapor Cloud Explosion algorithms
can handle deflagration and detonation.
A complete description of the algorithms used in the
flat terrain version of the software is
available.
A complete description of the algorithms used in the
complex terrain version of the software is
available.
A schematic of the processes considered within a grid cell for the complex terrain version is shown below in Figure 1.
Figure 1. Processes considered in the complex terrain version of CHARM..